Compression rings for column relief in continuous cooking vessels

ABSTRACT

The flow of a liquid slurry of comminuted cellulosic fibrous material (e.g. wood chips) in a vertical vessel is made more uniform by providing a plurality of vertically spaced sets of either substantially continuous or discontinuous protrusions which extend inwardly from the internal surface of the vessel a maximum distance of between about 2-12 inches. A preferred vessel is a continuous or batch digester. The protrusions may have an arcuate, rectangular, isosceles or scalene triangular, right triangular, or trapezoidal cross-section, and may be spaced from each other vertically between about 1-12 feet, and have a height of between about 1-3 feet. Discontinuous protrusions have a preferred arcuate spacing of between 1-10 feet.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on provisional application Serial No.60/104,401 filed Oct. 15, 1998, the disclosure of which is incorporatedby reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] U.S. Pat. No. 5,454,490 entitled “CONICAL INSERTS FOR CHIP BIN”discloses a method and apparatus for improving the flow of wood chipsthrough a vertical wood chip treatment vessel by introducing conicalrings to the interior surface of the vessel. These frustum-shaped ringsprovide relief of compaction forces due to the weight of the materialand promote the uniform movement and treatment of the chips in thevessel (typically referred to as a “chip bin”). However, the patent isprimarily directed to treating chips in a relatively dry state, wherebridging or compaction may occur. No liquids are typically present insuch bins, though one form of treatment disclosed is the introduction ofsteam to the bin.

[0003] In copending U.S. patent applications 08/936,047 filed on Sep.23, 1997 [atty. ref. 10-1214] and 08/953,880 filed on Oct. 24, 1997[10-1217] the movement through and treatment of cellulose material invertical continuous digesters is discussed. In particular, theseapplications (the disclosures of which are incorporated by referenceherein) discuss the various degrees of compaction that can occur in avertical column of comminuted cellulosic fibrous material (for example,wood chips) and how this compaction affects both the movement of thecolumn and the treatment of the material with treatment liquids,especially in the vicinity of the annular screen assemblies that are socommon to vertical continuous cooking vessels. The various embodimentsdisclosed in these applications show how the movement and treatment canbe made more uniform by introducing novel screen assembly geometries.The present invention also improves the uniformity of the movement ofmaterial in treatment vessels and thus improves the uniformity of thetreatment.

[0004] Surprisingly, according to the invention it has been discoveredthat the vertical movement of comminuted cellulosic fibrous materialslurries, such as wood chips slurries, can be improved (e.g. made moreuniform) by providing protrusions on the internal substantially verticalsurface of the cooking vessel. These protrusions may be substantiallycontinuous, that is, substantially annular, or may be intermittentlydistributed about the circumference of the internal surface of thevessel. In one embodiment, the protrusions consist of or comprise one ormore substantially annular rings. In another embodiment, the protrusionsconsist of or comprise one or more rows of two or more individualstructures evenly distributed or non-evenly distributed about thecircumference of the internal surface of the vessel. The protrusions(also called protuberances) may be aligned in one or more rows, or onerow of protuberances may be off-set from an adjacent row. One or aplurality of rings or rows may be used in any part of a treatmentvessel, for example, a digester, where column movement may be a problem.This includes in the top of the vessel, in the middle of the vessel, andin the bottom of the vessel.

[0005] Though the mechanism by which these protuberances promote theuniform movement of the cellulose material is uncertain, it is believedthat the protuberances provide a temporary relief of the compressiveforces within the column and thus the temporary relief of the normalforces on the internal surface of the vessel so that friction betweenthe chip mass and the vessel wall is temporarily decreased orsubstantially eliminated. It is believed that this reduction in frictionpermits the cellulose material to more uniformly flow through thetreatment vessel and allow more uniform treatment of the material.

[0006] The protuberances or substantially annular rings of the inventionmay take a variety of shapes or geometries. The geometry of the ringsmay take any form, but is typically a geometry that does not extend morethan about one foot [0.3 meter] from the internal surface of the vessel[the vessel typically has an interior diameter of between about 10-40feet]. In a preferred embodiment, the protuberances or rings do notextend more than about 4 inches [10 cm] from the vessel surface,preferably not more than about 2 inches [5 cm] from the surface. Apreferred embodiment of the rings or protuberances is one having a taperin the direction of the movement of the material such that the upperinternal diameter or radius of the protuberance or ring is greater thanthe lower internal diameter or lower internal radius of the ring orprotuberance. The protuberance or ring preferably has a taper angle ofabout 70 degrees or less, typically 45 degrees or less, but ispreferably 15 degrees or even 10 degrees or less, e.g. between about5-15 degrees. The protuberance or ring may have a height of 3 feet [1meter] or less, but is preferably 1 foot [0.3 meter] or less in height,e.g. about 0.5-3 feet [0.15-1 meter]. If two or more rings or rows areused, the rings or rows may be separated by 12 feet [4 meter] or more,or may be separated by only 6 feet [3 meter] or even 3 feet [1 meter],or only 1 foot [0.3 meter], e.g. between about 1-12 feet [0.3-4 meter].

[0007] The one or more rings or protuberances may be made from anyappropriate material, for example, carbon steel or stainless steel or anickel alloy, or plastic, for example Dupont Teflon®, or a Teflon®containing plastic, or having a polytetrafluoroethylene or like lowfriction material coating. They may be secured to the shell by any formof appropriate fastening, for example, they may be attached by welding,or adhesive, or by one or more mechanical fasteners (e.g. threadedfasteners).

[0008] In one embodiment of the invention, the one or more (e.g. 1-10)annular rings or protuberances are metallic and perform the dual role ofenhancing column movement and providing a cathode or anode for anodiccorrosion protection of the vessel.

[0009] According to one aspect of the present invention there isprovided a method of treating a liquid slurry of comminuted cellulosicfibrous material (e.g. at about 8-20% consistency) in a substantiallyvertical vessel having an internal surface, comprising: (a) Introducingthe slurry into the vessel so that the slurry moves substantiallydownwardly in the vessel in a column. And, (b) at a plurality ofvertically spaced locations in the vessel temporarily relievingcompressive forces within the column and the normal forces on theinternal surface of the vessel so that friction between the comminutedmaterial and the vessel internal surface is temporarily decreased, orsubstantially eliminated, providing more uniform flow of the material inthe vessel.

[0010] In the method (b) may be practiced to temporarily reduce thefriction by at least 20% (e.g. 20-99%). Typically (b) is practiced byproviding a plurality of vertically spaced compression-relieving surfacemanifestations on the internal surface of the vessel. For example, (b)is further practiced by providing at least one substantially continuousannular element having an inner surface that protrudes into the vesselfrom the internal surface a greater distance at a lower portion thereofthan at a higher portion thereof. That is, (b) may be further practicedby providing a curved inner surface; or a sloped inner surface having anangle with respect to the vertical of between about 5-15°; and/or (b) isfurther practiced by vertically spacing at least some manifestationsbetween about 1-12 feet, and by providing the manifestations so that themaximum radial spacing thereof from the internal surface is betweenabout 1-12 inches.

[0011] In one embodiment (b) is further practiced by providing at leastone surface manifestation with an inner surface which contacts theslurry column of a material having low friction properties substantiallythe same as polytetrafluoroethylene.

[0012] The method may further comprise (c) cooking the material of theslurry in the vessel at a temperature above 90° C. with a cookingliquid, e.g. by cooking the material with kraft cooking liquor atsuperatmospheric pressure and at a temperature above 100° C. (e.g.140-160° C.).

[0013] According to another aspect of the invention there is provided: Asubstantially vertical vessel having an internal surface comprising: Aplurality of vertically spaced sets of circumferentially discontinuousprotrusions extending inwardly from the internal surface a maximumdistance of about 1-12 inches. An inlet at or near a top portion of thevessel. And, an outlet at or near a bottom portion of the vessel. Forexample, the protrusions have an arcuate cross-section, or asubstantially isosceles or scalene triangular, or rectangularcross-section. Typically the protrusions have a height of between about1-3 feet, and a vertical spacing between at least two sets of betweenabout 1-12 feet. For example, at least two sets of protrusionsvertically spaced between about 1-12 feet have the protrusions thereofcircumferentially offset from one set to the next. Also the protrusionsmay be circumferentially spaced from each other between about 5-30°, andan arcuate distance of between about 1-10 feet.

[0014] According to another aspect of the present invention there isprovided a method of treating a liquid slurry of comminuted cellulosicfibrous material in a substantially vertical vessel having an internalsurface, comprising: (a) Introducing the slurry into the vessel so thatthe slurry moves substantially downwardly in the vessel in a column.And. (b) at a plurality of vertically spaced locations in the vessel,causing the slurry to flow over surface manifestations which extend intothe vessel a maximum distance of between about 1-12 inches. In themethod (b) may be further practiced by providing a plurality ofcircumferentially discontinuous protrusions at each of a plurality ofdifferent levels within the vessel. Other details and modifications maybe as described above.

[0015] According to yet another aspect of the present invention there isprovided a substantially vertical vessel having an internal surface, andcomprising: An inlet at or adjacent a top portion of the vessel. Anoutlet at or adjacent a bottom portion of the vessel. And, at least onesubstantially continuous annular protrusion connected to the internalsurface and in a substantially horizontal plane, and having a maximumspacing from said internal surface of between about 1-12 inches, theprotrusion having a cross-section selected from the group consistingessentially of right triangular, scalene triangular, isoscelestriangular, arcuate, and rectangular. The protrusions may have asubstantially isosceles triangular cross-section with an apex anglebetween about 90-175°, or may be arcuate in cross-section with a radiusof curvature equal to or greater than its height. The vessel may furthercomprise a plurality of the protrusions, vertically spaced from eachother between about 1-12 feet, and each having a height of between about1-3 feet.

[0016] It is the primary object of the present invention to provide amethod and vessel which effect more uniform flow (and thus typicallyuniform treatment) of material, such as cellulosic fibrous materialslurry, e.g., in a digester. This and other objects of the inventionwill become clear from the detailed description of the invention andfrom the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic side view, with the near wall portionremoved for clarity of illustration, of an exemplary continuous digesteraccording to the invention for practicing the methods of the invention;and

[0018] FIGS. 2-7 are detail schematic cross-sectional views of variousforms that the protrusions illustrated in FIG. 1 can take pursuant tothe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 illustrates a typical vertical continuous digester 10 inwhich the present invention is embodied or can be used. This digesterincludes an inlet 11 for a slurry of cellulose chips or the like andliquid, a conventional liquid separating device 12, a conventionalcentral pipe for distributing treatment liquid 13, one or moreconventional screen assemblies 14, 15, 16, and 17 for removing liquidform the slurry, an outlet 18, and a vessel shell 19 having an internalsurface 20. According to the present invention the vessel shell 19 alsoincludes one or more rings, or rows, of protuberances. 21, 22, 23, 24,25, 26 and 27. These rings, or rows, of protuberances, may be located inany part of the vessel where column movement may be effected.

[0020]FIGS. 2 through 7 illustrate various exemplary geometries of therings or protuberances 21 through 27 shown in FIG. 1 for the vesselshell 19 having an internal surface 20. FIG. 2 illustrates a single ring28 having a convergent angle 29 of between about 5-25 degrees to thevertical, preferably between about 5-15 degrees. The length of thevertical surface 30 may be from 1 to 90% of the height 31 of the ring28. There may also be no vertical surface 30.

[0021]FIG. 3 illustrates another ring 32 geometry similar to FIG. 2having a convergent angle 33 between about 10 and 70 degrees to thevertical, preferably between about 40 to 50 degrees, most preferablyabout 45 degrees. The vertical surface 34 may extend from 1 to 90% ofthe length 35 of the ring 32. There may also be no vertical surface 34.

[0022]FIG. 4 illustrates another ring 36 having no tapered edges butsimply having a rectangular cross-section.

[0023] The structures shown in FIGS. 2, 3 and 4 may represent thecross-sections of substantially continuous annular rings (23-27 in FIG.1), or of two or more individual protuberances spaced circumferentiallyfrom each other (see 21 and 22 in FIG. 1) that may be used according tothe present invention. When the protuberances in a set arecircumferentially spaced from each other, the circumferential spacing istypically between about 5-30°, with a spacing arcuate length of betweenabout 1-10 feet.

[0024]FIG. 5 illustrates an embodiment having three curved annular (ordiscontinuous) protuberances 37, 38, and 39 substantially equally spacedfrom each other vertically. That is the protrusions 37-39 have asubstantially arcuate cross-section. The radius of curvature 40 of thecurved surfaces may vary as required (e.g. be substantially equal to orgreater than the height 49 of the associated protuberances 38). Theradius of curvature of adjacent rings or protuberances 37-39 may bedifferent, or the same.

[0025]FIG. 6 illustrates another set of annular rings or protuberances41, 42 having a triangular cross section. The triangular section may byisosceles in cross section, as shown, or may be scalene in crosssection. The angle 43 of the apex of the triangle cross section may varyfrom between 10 to 179 degrees, but is preferably between about 90 and175 degrees. The apex angle 43 of adjacent rings or protuberances may bedifferent from each other, or the same. FIG. 7 illustrates a single rowor ring 44 similar to the rings 41, 42 of FIG. 6.

[0026] The typical height of a protrusion, e.g. the height 46 forprotrusion 37 (in FIG. 5), is between about 1-3 feet, and the verticalspacing between some protrusions, e.g. the spacing 47 (FIG. 5), ispreferably between about 1-12 feet. The spacing 48 may be the same as,or different from, the spacing 47, and the heights 49, 50 may be thesame as or different from the height 46, and from each other.

[0027] The protrusions shown in any of the drawing figures may be ofmetal, such as carbon steel, stainless steel, nickel alloy, or the like,or may be plastic. They may comprise, include, be coated with, orcontain a low friction material such as a material having low frictionproperties substantially the same as polytetrafluoroethylene (likepolytetrafluoroethylene itself). In one embodiment of the invention, theone or more (e.g. 1-10) annular rings or protuberances are metallic andperform the dual role of enhancing column movement and providing acathode or anode for anodic corrosion protection of the vessel.

[0028] Though the present invention is described above in reference to acontinuous digester (and use therewith is particularly advantageous), itis to be understood that the invention is applicable to any type ofvessel 19 in or through which particulate material is stored, treated ortransferred, for example, cellulose pulp digesters, continuous or batch;storage towers or vessels; treatment towers, for example, bleach towers;chip bins; grain silos; and other similar vessels. While also applicableto dry material, the constructions are particularly useful inassociation with liquid slurries, e.g. having consistencies betweenabout 1-40% (e.g. between about 8-20%).

[0029] Thus, according to the present invention a method and apparatusfor improving the movement of cellulose material through treatmentvessels and improving the treatment of cellulose material in thosevessels is provided. While the invention has been described inconnection with what is presently considered to be the most practicaland preferred embodiment, it is to be understood that the invention isnot to be limited to the disclosed embodiment, but on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of this specification, including,but not limited to, all narrower ranges within a broad range (e.g.between 1-12 feet means 2-4 feet, 3-8 feet, and all other narrowerranges between 1-12 feet). Also conventional equivalents of allcomponents discussed above may be substituted.

What is claimed is:
 1. A method of treating a liquid slurry ofcomminuted cellulosic fibrous material in a substantially verticalvessel having an internal surface, comprising: (a) introducing theslurry into the vessel so that the slurry moves substantially downwardlyin the vessel in a column; and (b) at a plurality of vertically spacedlocations in the vessel temporarily relieving compressive forces withinthe column and the normal forces on the internal surface of the vesselso that friction between the comminuted material and the vessel internalsurface is temporarily decreased, or substantially eliminated, providingmore uniform flow of the material in the vessel.
 2. A method as recitedin claim 1 wherein (b) is practiced to temporarily reduce the frictionby at least 20% for a slurry with a consistency between about 8-20%. 3.A method as recited in claim 1 wherein (b) is practiced by providing aplurality of vertically spaced compression-relieving surfacemanifestations on the internal surface of the vessel.
 4. A method asrecited in claim 3 wherein (b) is further practiced by providing atleast one substantially continuous annular element having an innersurface that protrudes into the vessel from the internal surface agreater distance at a lower portion thereof than at a higher portionthereof.
 5. A method as recited in claim 4 wherein (b) is furtherpracticed by providing a curved inner surface.
 6. A method as recited inclaim 4 wherein (b) is further practiced by providing a sloped innersurface having an angle with respect to the vertical of between about5-70°.
 7. A method as recited in claim 3 wherein (b) is furtherpracticed by vertically spacing at least some manifestations betweenabout 1-12 feet, and providing the manifestations so that the maximumradial spacing thereof from the internal surface is between about 1-12inches.
 8. A method as recited in claim 3 wherein (b) is furtherpracticed by providing at least one surface manifestation with an innersurface which contacts the slurry column of a material having lowfriction properties substantially the same as polytetrafluoroethylene.9. A method as recited in claim 3 further comprising (c) cooking thematerial of the slurry in the vessel at a temperature above 90° C. witha cooking liquid.
 10. A method as recited in claim 9 wherein (c) ispracticed by cooking the material with kraft cooking liquor at atemperature above 100° C., while it has a consistency of between about8-20%.
 11. A substantially vertical vessel having an internal surfaceand comprising: a plurality of vertically spaced sets ofcircumferentially discontinuous protrusions extending inwardly from saidinternal surface a maximum distance of about 2-12 inches: an inlet at ornear a top portion of said vessel; and an outlet at or near a bottomportion of said vessel.
 12. A vessel as recited in claim 11 wherein saidprotrusions are arcuate in cross-section.
 13. A vessel as recited inclaim 11 wherein said protrusions have a substantially isoscelestriangular cross section with an apex angle of between about 10-175°.14. A vessel as recited in claim 11 wherein said protrusions have asubstantially rectangular cross-section.
 15. A vessel as recited inclaim 11 wherein said protrusions have a height of between about 1-3feet, and a vertical spacing between at least two sets of between about1-12 feet.
 16. A vessel as recited in claim 15 wherein at least two setsof protrusions vertically spaced between about 1-12 feet have theprotrusions thereof circumferentially offset from one set to the next.17. A vessel as recited in claim 11 wherein the protrusions arecircumferentially spaced from each other between about 5-30°, and anarcuate distance of between about 1-10 feet.
 18. A method of treating aliquid slurry of comminuted cellulosic fibrous material in asubstantially vertical vessel having an internal surface, comprising:(a) introducing the slurry into the vessel so that the slurry movessubstantially downwardly in the vessel in a column; and (b) at aplurality of vertically spaced locations in the vessel, causing theslurry to flow over surface manifestations which extend into the vessela maximum distance of between about 1-12 inches.
 19. A method as recitedin claim 18 wherein (b) is further practiced by providing a plurality ofcircumferentially discontinuous protrusions at each of a plurality ofdifferent levels within the vessel.
 20. A method as recited in claim 3wherein (b) is further practiced by providing a plurality ofcircumferentially discontinuous protrusions at each of a plurality ofdifferent levels within the vessel.
 21. A method as recited in claim 18wherein (b) is further practiced by providing at least one substantiallycontinuous annular element having an inner surface that protrudes intothe vessel from the internal surface a greater distance at a lowerportion thereof than at a higher portion thereof, and (a) is furtherpracticed by introducing a slurry having a consistency between about8-20%.
 22. A substantially vertical vessel having an internal surface,and comprising: an inlet at or adjacent a top portion of said vessel; anoutlet at or adjacent a bottom portion of said vessel; and at least onesubstantially continuous annular protrusion connected to said internalsurface and in a substantially horizontal plane, and having a maximumspacing from said internal surface of between about 1-12 inches, saidprotrusion having a cross-section selected from the group consistingessentially of right, isosceles, or scalene triangular, arcuate, andrectangular.
 23. A vessel as recited in claim 22 wherein said protrusionhas a substantially isosceles triangular cross-section with an apexangle between about 10-175°.
 24. A vessel as recited in claim 22 furthercomprising a plurality of said protrusions, vertically spaced from eachother between about 1-12 feet, and each having a height of between about1-3 feet.
 25. A vessel as recited in claim 22 wherein said protrusion isarcuate in cross-section with a radius of curvature equal to or greaterthan its height.